Plumbing two new bathrooms one above the other and then to main stack?

I am adding a half bath on the first floor and a 3/4 bath on the second. They are stacked above and below each other. It will be all new plumbing on the left side branch of my drawing. Do you see any problems with my venting of the two baths together using a 3" stack? What fittings are necessary for the connections on each floor?

Horizontal distance from new stack (on the left) to main(original) CI stack where I will tie in is about 7feet. The new WC on the second floor will be about 3feet from the new stack so horizontal distance will be right around 10 feet total after all the drop.

Any wet venting has to be on the same floor, a bathroom group in a residence.

The toilet vent, or wet vent needs to happen before the waste from upstairs enters the line.
So the downstairs lav would need to wye in closer to the downstairs toilet, "before" the wye for the upstairs bath.

Also, the upstairs shower needs a vent between the it's trap arm and the stack below the toilet.
The vent needs to come off the top of the trap arm, you can't go up after a vent, except for the normal 1/4" per foot grade, within five feet.

Attached Files:

You started with a "simple" design which needed a few revisions and have created a "monster". The "second" drawing is completely wrong because you cannot connect the vent back below the upstairs bath. From you drawing it appears you are putting the pipes below the joists so you can use a side inlet "T" for the lav and shower inlet. This is NOT the place to give you a tutorial on installing drains and vents, but if it were I, I might throw your entire drawings away and start over with a much simpler design than any of them.

I understand this is not a tutorial site. Too much time last night I guess. I was searching the forum for examples and found someone else's example that was "approved" and modified it by removing bath from first floor bath to match my intentions. Came up with all sorts of monsters.

In the original drawing I was using a t for the horizontal lav to sink inlet. The shower drain is less than three feet from the new vent stack. I can run that by itself to a wye to connect it without combining them. The stack would qualify as the vent for the shower since it is so close.

quote; The stack would qualify as the vent for the shower since it is so close.

NOT NECESSARILY. That is like saying that milk will not spoil if it is on the table close to the refrigerator. IF the shower's Y is between the vent and the toilet, then the stack will NOT, nor can it, be the shower's vent.

quote; The stack would qualify as the vent for the shower since it is so close.

NOT NECESSARILY. That is like saying that milk will not spoil if it is on the table close to the refrigerator. IF the shower's Y is between the vent and the toilet, then the stack will NOT, nor can it, be the shower's vent.

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Are you meaning that if the shower's Y is on the horizontal between the WC and the vent it would need its own vent?

What I meant was I would go directly to the stack with its own sani-T rather than combine with the horizontal line from the WC/lav. Either stack two sani-T fittings vertically or use a sani-T hub (which I do not know if it is ok and asked about it in another thread).

It is mightily difficult to tie in the lav vent to the 3 inch stack in the attic but simpler just to have another roof penetration instead. How the shower branch connects and vents is what is left to figure out. Use sani-T hub, two vertical sani-T's or ? Without the shower the second floor plumbing looks like this so far. The shower is 90 degrees from the direction the WC comes in (hence the 3x3x3x2 hub thought).

Options:
1.Use a combo sani-T hub 3x3x3x2 (would simplify things). Stack acts as vent for the shower.
2.Use a vented branch to a 3x3x2 sani-t. Venting required for the drop to get below the wc connecting sani-T.
3. Connect shower to lav waste via a Y fitting and add 2" vent near connection to3" Y between WC and stack vent. (Tie into WC 2" vent or into stack on its own?)
First Option:
Second Option:
Third Option:

I don't know how much "flexbility" you have as far as the pipe installation goes, but if it could be done, I would install the 3" stack at the lavatory with the 3x3x3x2 tee below it. Run the shower into the side, "offset" the toilet to its required location, and use a 3x1 1/2" tee for the sink. The way you have it drawn, however, NONE of the installations need the 2" vent at the toilet. Third option, neither the 2" for the toilet, nor that "cosmetic" vent on the sink/shower drain is necessary. There could be other possible "easier" layouts, if we knew the floor plan and fixture locations, or if you have a great deal of latitude on where the fixtures will be located, which seems to be case according to your various drawings.

The projects are in the garage and the bonus room above the garage utilizing a dormer area for a shower. The proposed 3" stack location is firm. The space above the stack in the kneewall is 50 inches tall. I can route it up the rafters to exit above the dormer valley. It lines up with vertically with the proposed bathroom wall below and the route to the basement to tie into CI stack. Nothing is framed on either floor, hence some flexibility. The hole through the poured concrete foundation on the first floor has been cut to access the CI stack in the basement.

Attached Files:

Thanks for pointing out the increase to 2" vent from the lav for the wet vent. As indicated by hj I would simplify the design and remove the 2" for the toilet and the "cosmetic" vent on the sink/shower drain, also.

Thanks! I see you kept the 2" vent on the WC on the second floor (hj indicated it was uneccessary but both of you do not always agree). I can easily keep it. Does the first floor require adding similar venting at the WC or is the wet vent from the sink adequate?

Note: I also have planned a cleanout on the bottom of the vertical stack even though it is not indicated on the drawing.

Use the side inlet tee for the toilet and shower, (without ANY individual vents), then run the sink to the separate Y installed below it.

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I will use the side inlet tee as that is a very short run for the shower and simple. Is there an argument for running the sink waste to a sani-T vs the wye connection after the WC? Maybe as a "better" plan to isolate the WC? I think using the wye on the WC seems simpler to plumb.

Either way is suitable. Lav to Y the stack is the vent for the shower and the lav is the wet vent for the toilet. Lav to T, the stack is the vent for the shower and the toilet and the sink has its own vent.